I believe I had some weird flickering where both Ale and coc.nvim were trying to report the same error. Coc.nvim through the tsserver extension, and Ale via eslint. I could see one of the error messages flash quickly before being replaced with another.

I’m sure there is a solution to that problem, but because coc.nvim supported eslint + prettier via extensions, I was able to reduce the amount of plugins I used by just relying on coc.nvim for linting/fixing.